Fujifilm X100 has a 12.0MP APS-C (23.6 x 15.8 mm ) sized CMOS sensor and features EXR processor. On the other hand, Samsung NX300M has a 20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features DRIMe IV processor.
Samsung NX300M's sensor provides 8MP more than Fujifilm X100's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Fujifilm X100's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the X100 and NX300M sensor size comparison.
Fujifilm X100 and Samsung NX300M have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.